1. Field of the Invention
This invention relates to an aerosol valve assembly and method of making an aerosol container and more particularly to an aerosol valve assembly of the type that is used to dispense viscous and semi-liquid material, such as whipped cream, hair styling mouse, shaving cream, etc., from within individually sized, hand carried, pressurized dispenser containers.
2. Discussion of the Prior Art
Known aerosol valve assemblies that are used to dispense semi-liquid and viscous materials, such as whipped cream, hair styling mousse, shaving cream and the like from individually sized pressurized containers of a size on the order of six to sixteen ounces employ a hollow, elongate, valve stem through which the material must pass when the valve is open. The material passageway through the hollow valve stem is relatively restricted, having a diameter of approximately only 1.0 millimeter.
The upstanding hollow valve stem is movably mounted to a mounting cup that, in turn, is fixedly seated in a central mounting hole of the top of a pressurized container of material to be dispensed. The mounting cup has an open circular top joined to a substantially flat circular bottom by a generally cylindrical wall. The flat bottom supports an upstanding tubular neck with a central, circular, mounting hole at its end. Fixedly contained within the neck is a resilient grommet with a central hollow, valve stem-mounting bore that opens at a valve seat within the container. A valve closure body at the end of the hollow valve stem presses against the valve seat to close the valve.
When the outside, distal end of the hollow valve stem is forced inwardly toward the container sufficiently to move the valve closure body away from sealing contact with the valve seat, the valve is actuated to an open position. In the open position the material, under pressure by virtue of the gas propellant, flows past the valve head and into the hollow valve stem at inlet openings to the material passageway that is defined by the hollow valve stem. The material flows through the inlet openings adjacent the valve closure member and through the hollow valve stem and out the open outlet end of the hollow valve stem.
Thus, the hollow valve stem is the actual conduit for the material being dispensed. An example of a valve of this general type but adapted for tilt operation of the hollow valve stem without use of a dispensing actuator is shown in U.S. Pat. No. 4,805,813 issued of Feb. 21, 1989, to Metcoff and the present inventor for "Aerosol Tilt Valve Mounting Cup And Assembly" to which reference should be made for further details of the basic construction and operation of the know aerosol valve assembly.
In this known valve assembly, it is of utmost importance, and special care is taken, that none of the material be allowed to enter into the valve stem mounting bore of the resilient grommet. Any material that passes through the bore simply messes the inside of the cup and is not received at the inlet end of dispensing actuator from the valve outlet opening at the end of the hollow valve stem. Accordingly, the relative dimensions are selected to insure a tight seal against such entry by means of continuous tight contact between the cylindrical outside surface and the cylindrical inside surface of the stem mounting bore throughout the length of the bore.
In the case of non-tilt valves that employ a dispensing actuator, the hollow valve stem extends upwardly above the open top of the mounting cup. Consequently, the relatively inflexible and fragile plastic hollow valve stem is only protected against breakage when the dispensing actuator is attached in protective covering and valve stem stabilizing relationship with respect to the valve stem. For this reason, the known valve assemblies are subject to breakage of the upwardly extending hollow valve stems during shipping, if shipped apart from the protective, dispensing actuator. Accordingly, separate shipping of valve assemblies is not performed in the ordinary course, and, instead, the valve assemblies are not shipped until attached to the pressurized containers and protected by attached dispensing actuators.
The known dispensing valve actuator has an elongate, hollow dispenser body pivotally mounted to a mounting collar that is snap fit over the edge of a rolled shoulder of the valve mounting cup. The elongate dispenser body has a relatively enlarged diameter that extends from a relatively enlarged inlet adjacent the mounting collar to a relatively distal, relatively enlarged distal outlet opening. The relatively enlarged inlet opening is connected in fluid communication through a relatively small diameter conduit transversely joined with a relatively small diameter hollow actuator.
The relatively small diameter hollow actuator slideably fits over the relatively narrow diameter, outlet end of the hollow valve stem to receive the material within its hollow body and convey it to a distal dispensing outlet opening.
When the hollow valve actuator is pressed down toward the container, the downward force is conveyed to the hollow valve stem to open the valve. When the valve is opened, the material within the aerosol container passes through the relatively small diameter hollow valve stem, the relatively small diameter hollow valve actuator member and the relatively small diameter conduit before connecting with the inlet end of the relatively large diameter dispenser body. The conduit interconnects the elongate, hollow dispenser body and the hollow valve actuator in a direction that is transverse to both of their elongate axes.
The inner diameter of the hollow valve stem is the smallest, being approximately 1-millimeter. The inner diameter of the hollow valve actuator and the conduit from the hollow valve actuator to the dispenser body is approximately only 4-millimeters. However, the diameter of the hollow dispenser body is approximately 10-millimeters--ten times that of the hollow valve stem.
The present inventor has determined that as a consequence of the "bottle neck" inherent in the above described designs of the known aerosol valve assembly and the associated dispensing aerosol valve actuator, for a given size container, the minimum amount of pressure needed to achieve an adequate flow rate must be much greater than would be needed if the cross-sectional area of the smallest diameter passageways were enlarged. Such enlargement facilitates the flow of material from the interior of the container to the relatively large cross section, elongate, hollow, dispenser body and reduces back pressure and the minimum pressure level needed to achieve adequate flow rate of material when the valve assembly is in an open state. In the case of existing valve assemblies used in conjunction with whipped cream containers, when the pressure within the container drops to approximately 90-psi, the flow rate of material is substantially slowed relative to the initial flow rate. After the pressure has been reduced to approximately 40-psi, then sealing between the valve stem mounting grommet and the flat bottom of the mounting cup is sufficiently reduced that leakage of the whipped cream often ensues.
On the other hand, the initial pressure must be sufficient to dispense all of the material within the container. This must be done even after most of the material has been dispensed and the volume available to the propellant gas has increased to thereby decrease the remaining pressure. The smaller the "bottle neck" caused by the relatively small diameter elements, the greater the pressure required to force the material out of the container through the valve and then out through the valve dispenser.
The inventor has also observed that because of the flat bottom design of the known mounting cups, this low pressure problem cannot be solved simply by increasing the level of the initial pressure, although unsuccessful attempts have been made.
There is a limit to which the known aerosol containers are capable of being initially pressurized without causing commercially unacceptable problems. The inventor has noted that if this limit is exceeded, then there is a risk of outward bowing distortion of the flat bottom of the mounting cup and resultant creation of gaps in the normal continuous contact seal between the valve mounting cup and the valve stem mounting grommet.
As noted above, the valve mounting cup has a generally cylindrical shape with a flat bottom, when made, and care is taken to ensure that when installed the pressure of the container is not sufficiently great to bend upwardly or otherwise distort the flat bottom. The substantially flat bottom extends in a plane from the central opening all the way to the perimeter side wall. Because of this configuration, the inventor has determined the flat bottom has a tendency to bow upwardly in response to the internal pressure acting in a single direction across the entire bottom. Such bowing of the flat bottom creates leaks between the bearing shoulder above the valve seat and the cup bottom resulting in material passing between the sides of the tubular neck within which the grommet body is mounted and bypassing the dispenser body.
Also, if the standard one mil thickness of the mounting cup is increased to prevent bowing of the flat bottom, despite the increased cost and weight caused by such thickening, excessive initial pressure applied to the container during pressure loading of the container is capable of loosening the seal between the mounting cup and the container.
The amount of pressure that the valve assembly can withstand places an upper limit on the quantity of dispensable material that can be contained within a pressurized container of given size. Thus, an approach of carefully pressurizing the containers to avoid any distortion of the flat bottom of the mounting cup is a further limitation on the maximum amount of material that a given sized aerosol container is capable of dispensing.
More specifically, the known aerosol valve assembly of the prior art functions satisfactorily only in relatively low pressure applications in which the initial internal pressure of the container is in the range from 130-psi to 140-psi. When the pressure drops approximately 50 to 60-psi, due to use, to a range of 70 to 80-psi, then the rate of dispensing is substantially slowed relative to the initial flow rate when at maximum pressure. This is due in part to the "bottle neck problem caused in part by the small valve opening, noted above. When the pressure drops further to approximately 40-psi, then the valve begins to lose the seal between the valve head and the valve stem and the valve begins to leak. Because of the disadvantageous features that have been discerned by the present inventor, the known aerosol valve assembly is less than entirely satisfactory in its performance when the pressure is in a range from 90-psi to 40-psi and is completely unsatisfactory when the pressure drops below 40-psi.
The amount of material that can be dispensed from the pressurized container is limited by the amount of propellant available. The amount of dispensing propellant that can be placed in the container is directly proportional to the internal pressure. Consequently, the inability of the known aerosol valve assembly to function well under relatively low pressure conditions creates a practical limit on the amount of material that can be usefully stored within a container of any given size. It is wasteful to place more material in the container than the maximum that can be dispensed from the container.
The inability of know valve assemblies to withstand higher pressures prevents increasing the initial pressure into a range to enable sufficient pressure for good flow rates for all the material being dispensed while eliminating leakage due to pressure decreases beneath the minimum needed for proper sealing of the valve stem grommet against the bottom of the mounting cup and closure of the valve head against the valve seat.